Fixed flatten docs (I think) (#25544)
Summary:
I think...
I'm having issues building the site, but it appears to get rid of the error.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/25544
Differential Revision: D17157327
Pulled By: ezyang
fbshipit-source-id: 170235c52008ca78ff0d8740b2d7f5b67397b614
